Study On Application And Technology Of Field-Flow Fractionation

Field-flow fractionation is a kind of particle separation technology on the micrometer and nanometer scale. There are several common methods of field-flow fractionation (FFF) such as sedimentation field-flow fractionation (SdFFF), gravitational field-flow fractionation (GFFF), thermal field-flow fractionation (ThFFF) and electric field-flow fractionation (EFFF). Aiming at the blank field of our country and the existing problems of foreign countries on FFF technology, the paper research the theory of FFF, the computer simulation of FFF, the manufacturing process of FFF channel, the detection method of FFF and the application of GFFF.1. Analyzing the basic principles and theoretical composition of FFF and summarizing the current at abroad2. Discussing the reasons of deviation caused by classical FFF theory3. Researching on the lifting force model of particle in the computer simulation of GFFFThe dimension parameters of separation channel is 300mm×20mm×400μm (length×width×highness). The simulation samples are PVC particles with the density of 1350kg/m3 and the sphere diameters of such particles are 6μm, 10μm and 15μm separately. The density of carrier fluid is 1000kg/m3 and the dynamic viscosity is 1.005×10-3Pa·s.The simulation result shows that the particle retention increases as the flow velocity of carrier fluid increases.Comparing the elution time of PVC particle obtained by simulation and the one by experiment, the experiment value agrees well with the simulation one when the sample size is about 30μm. The deviation between experiment value and simulation one varies regularly especially the greater the deviation between sample dimension and the value of 30μm is, the higher it is. When the dimension is less than 30μm, the deviation is positive which means the practical eluting time is longer than the simulation one and vice versa.The paper researches the flow characteristic of different geometric shapes of FFF channel's entrance by use of computer simulation. Comparison with different entrance shapes-round, circle, ellipse and triangle of different angles, we find the best entrance shape is triangle and the hemline vs. height should be 1:1.4. Having developed several manufacturing process for making flow channels which are used for EFFF channel, GFFF channel, SdFFF channel, gravitational-thermal FFF channel and micro thermal FFF channelThe paper studies two new kinds of manufacturing process of GFFF channel.1.) Direct clamping processPartly based on foreign manufacturing process, we obliterate the original clamped plate and replace the super-flat glass which is used for the upper and lower channel plate with grinded steel plate. The experiments prove that the GFFF channel manufactured by our process can completely come up to requirements. It is much simpler than the foreign manufacturing process and more suitable in industrial production. Certainly there is some defection that the separation channel wall has the tendency to be rotted. 2.) Hot molding and hot embossing process After selection of two pieces of copper the thicknesses of which are 0.25mm and 0.6mm separately, we cut them into hot molding plates of GFFF separation channel with numerical control line cutting machine and then polish into 517μm and 212μm separately. The selection of hot molding material is PMMA and its glass temperature 105℃. We adopt sketch map of 769 YP-15A imprinting machine as hot molding equipment. Owing to the detailed size of pressing block is smaller than the required one of hot molding work piece, we take two pieces of auxiliary pressing board and adopt the method of step molding.After several groups of experiments with different pressure, temperature and holding time, we get the better parameters of hot molding are 3.5MPa, 104℃, and 60min. When the hot molding temperature is higher than the glass temperature, the thermal deformation of separation channel plate is severe and is not good for application. With the parameters above, the reduction volume of the thickness of GFFF channel acquired is less than 10% compared with the thickness of molding. Although the reduction volume will increase if reduce the recommended pressure and holding time, we can also get the needed separation channel thickness by increasing the template thickness and the thicker template is more convenient to produce.Using the process above in the making separation channel, it is not convenient to pull out the template after molding. For this we develop one new process of template making. In detail, we use the grinding machine to grind the boss on the template. The practice proves that this method is efficient. After alcohol disposal on the embossed surface, we carry out hot embossing with the parameters as follows: board temperature with flow channel 80℃; board temperature without flow channel 76℃; pressure 1.5MPa; thermo-pressure time 90s. The separation channel after hot embossing meets the FFF requirements and the contraction volume of the thickness of GFFF channel acquired is less than 10%.5.Designing one set of digital image detection system for FFFThe system includes hardware and software of image processing. The latter partly adopts the digital image processing software from Basler Company and the remaining part is self-development. Using the system for the GFFF off-line detection of wheat flour, the experiment obtains the three ranges of dimension of wheat flour distribution. Aiming at the high cost of FFF detection apparatus, the paper proposes one new method-resistance detection method. This measuring method is designed in view of the characteristics of resistance which change along with that weather there is or not separated components in the FFF carrier fluid. Concretely speaking, we put in series the resistance (180k?) to a part which is 9mm long in the outflow tube of the separation flow, and then put 6V DC voltage in the end of series circuit and acquire the voltage change in the end of the resistance with the Data Acquisition System. We apply this measuring method to detect the wheat flour separation in the GFFF. For the measuring result is equal to the one measured by Image Detection, we come to the conclusion that this detection method is feasible.6. Developing the application study of GFFFBy analyzing the linear dimension of the active ingredients of Chinese traditional medicine, we find that it is just in the application area of FFF. Considering the present conditions of our laboratory, we carry on the research on the GFFF separation of Chinese traditional medicine powder. During the experiments we take Niuhuang Qingfei San as separate sample, organic glass as the material of separation channel and a single tube stereoscopic microscope as the tool of on-line observation. At the same time, the separate image can be acquired through CCD. Based on the experiments we observe that the large sample particles have a higher velocity than the small ones in the separation channel, and the sample dimensions observed simultaneously are almost equal. These prove that GFFF can be fully used in the separation of Chinese traditional medicine powder and its practical significance is that it provides one effective method to analyze the relationship between the dimensions of components inside Chinese medicine powder and drug efficiency.Still the paper studies the application of GFFF in the separation of the organic matter and the mineral. The organic matter and mineral adopt wheat flour and iron ore as separate sample separately. In the separation experiments, the wheat flour separation is completed within 10min and it is divided into three similar groups by dimension after GFFF whereas because the iron ore powder can't move with the carrier fluid even at the velocity of 99.9mL/h, the separation can't be completed. So one self-made larger flow pump, pump flow is up to 704mL/h, is used to complete the separation of iron ore powder successfully. It is found that the flow velocity of carrier fluid should reach a certain value to complete GFFF of the high-density, non-spheroid and micrometer particles. As far as the relationship among the sample density, the sample geometry shape and the carrier fluid velocity it is still waiting for the further research.